/*
db库
 */
var MongoClient = require('mongodb').MongoClient;
const ObjectID = require('mongodb').ObjectID;
var Config = require('./config.js');
var fs = require('fs');
var mongo = require('mongodb');

class Db {
    static getInstance() {  //单例
        if (!Db.instance) {
            Db.instance = new Db();
        }
        return Db.instance;
    }

    constructor(){
        this.dbClient = ""; //放db对象
        this.connect();
    }

    connect(){
        let _that = this;
        return new Promise((resolve, reject) => {
            if (!_that.dbClient) {  //解决数据库多次连接问题
                MongoClient.connect(Config.dbUrl, {useUnifiedTopology: true}, (err, client) => {
                    if (err) {
                        reject(err);
                    } else {
                        _that.dbClient = client.db(Config.dbName);
                        resolve(_that.dbClient);
                    }
                })
            } else {
                resolve(_that.dbClient);
            }
        })

    }

    find(collectionName, json){
        return new Promise((resolve, reject) => {
            this.connect().then(db => {
                var result = db.collection(collectionName).find(json);
                result.toArray((err, docs) => {
                    //console.log(docs);
                    if (err) {
                        reject(err);
                        return;
                    }
                    resolve(docs);
                })
            })
        })
    }

    update(collectionName, json1, json2){
        return new Promise((resolve, reject) => {
            this.connect().then(db => {
                db.collection(collectionName).updateOne(json1, {
                    $set: json2
                }, (err, result) => {
                    if (err) {
                        reject(err);
                    } else {
                        resolve(result);
                    }
                })
            })
        })
    }

    insert(collectionName, json){
        return new Promise((resolve, reject) => {
            this.connect().then(db => {
                db.collection(collectionName).insertOne(json, (err, result) => {
                    if (err) {
                        reject(err);
                    } else {
                        resolve(result);
                    }
                })
            })
        })
    }

    remove(collectionName, json){
        return new Promise((resolve, reject) => {
            this.connect().then(db => {
                db.collection(collectionName).removeOne(json, (err, result) => {
                    if (err) {
                        reject(err);
                    } else {
                        resolve(result);
                    }
                })
            })
        })
    }

    getObjectId(id) {   //字符串转化为对象
        return new ObjectID(id);
    }

}
module.exports = Db.getInstance();
/*
//测试
var myDb = new Db();
myDb.find("user",{}).then(data => {
    console.log(data);
})
 */